This invention relates to a hydrodynamic stirring device to dissolve, mix or put back into suspension or into a xe2x80x9csolxe2x80x9d, in a primary liquid phase, a sediment which is contained in a tank and covered by said primary liquid phase.
Equipment for cleaning oil tanks including rotary lances having fluid ejection nozzles is known from the state of the art patent U.S. Pat. No. 5,087,294. These nozzles are radially orientated and require that the nozzle carrier be driven by a motor.
A hydrodynamic stirrer, disclosed by patent EP 0 160 805, is also known in the state of the art, wherein the device comprises, in one of the alternative embodiments, a self-rotating lance fitted with nozzles directed orthogonally with respect to the axis of rotation of the rotor, so as to project horizontal jets. An additional nozzle is directed at about 45xc2x0 with respect to the axis of rotation, to form a jet of liquid angled downwards.
The disadvantage of the device of the prior art is that the tubes, at the bottom ends of which the self-rotating lances are connected, have a tendency to fracture in the region of their upper end, where they are attached to the roof of the tank. This fracturing is apparently due to the fact that the tubes which may have a length of from 15 to 20 meters, are subject to bending forces, the direction of which varies at every instant as a function of the angular position of the rotor of the lance. The result is fatigue in the lance that may bring about the fracture or at least cracking of the lance or the tube which is supporting it, which then causes a major malfunction of the device.
This invention provides a remedy to these drawbacks by providing a self-rotating hydrodynamic stirring device that is robust and reliable. To this end, the invention in its most general form relates to a device fitted with nozzle bearing lances, having nozzles arranged in such a way that the resultant of the radial components is canceled out.
In accordance with one preferred embodiment, the nozzles are arranged in angular directions and with orientations such that the axes of their respective orifices are deduced from one another by rotation through an angle of 360xc2x0/n about the central axis of the nozzle bearing rotor, wherein n is the number of nozzles located on the periphery of the nozzle bearing rotor.
According to one particular alternative, each of the nozzles located at the periphery of the nozzle bearing rotor has an orifice, the axis of which forms an angle of about 30xc2x0 with respect to the radius corresponding to the angular position in which the nozzle under consideration is to be found.
According to one preferred embodiment, the axes of the orifices of the nozzles are offset laterally with respect to radial longitudinal planes. Under the term xe2x80x9cradial planexe2x80x9d, a plane is understood, defined by the longitudinal axis of the nozzle carrier on the one hand, and by a radial axis perpendicular to the longitudinal axis, the radial axis being parallel to the median axis of the orifice of the nozzle. The median axis of the orifice of a nozzle is not in a radial plane, but in a plane parallel to a radial plane.
Advantageously, the device comprises two nozzles, the orifice axes of which are parallel and laterally offset on either side of a median plane formed by a diametrical axis and the longitudinal axis. The lateral offset between the axis of the orifice of the nozzle carrier and the plane formed by a radial axis and the longitudinal axis is preferably between about 8 and about 14 mm, and preferably about 9 mm.
According to one particular embodiment, the device comprises three nozzles each having an orifice with a diameter of about 5 mm, the third nozzle having its axis merged with the axis of rotation of the nozzle bearing rotor.